1. Field of the Invention
The present invention relates to an apparatus for playing back an optical recording medium and, more particularly, to a digital disc player capable of reproduction both from a digital versatile disc (DVD) and a compact disc (CD).
2. Description of the Related Art
MEPG2 video/audio information compression techniques have been improved to a practical level, and the development of DVD players for reproducing images and sounds recorded on DVDs of the CD size using techniques of this kind are being promoted. A DVD loaded in such a DVD player has one or two signal recording surfaces formed on one side. Holes ("pits") are formed in each signal recording surface. There are several types of pit, differing in length. A track is formed by arranging such pits differing in length. During reproduction (play back) of a signal recorded on the disc, the pits are read along the track and various kinds of signal processing are performed on the read out signal to output video and audio signals.
Playback from the well-known CD is the same as that for a DVD with respect to signal reading along the sequence of pits formed on the disc, but differs in signal processing performed on the read-out signal.
On DVDs and CDs, signals are recorded by basically the same method. Also, basically the same signal reading method is used for DVDs and CDs. However, DVDs and CDs differ in both storage capacity and pit size. For example, a dual-layer DVD disc having two signal recording surface layers on one side has a capacity of 8.5 gigabytes, and a single-layer DVD disc having one signal recording surface layer has a capacity of 4..7 gigabytes. On the other hand, CDs have a capacity of about 780 megabytes. With respect to the pit size, both the length and width of DVD pits is approximately half that of CD pits.
As described above, DVDs and CDs differ from each other in the size of the pits formed in the signal recording surface. Therefore, if these two kinds of discs are played back by one dual mode player, changing the numerical aperture of an objective lens and the amplification factor of an RF amplifier in the player as well as other operations are required. As a prerequisite for such changes, identification of the kind of a disc as a DVD or CD actually loaded in the player must be made.
However, since DVDs and CDs are the same in contour and size, a user of the disc player cannot discriminate between a DVD and a CD from the external appearance of the disc, and may fail to indicate to the disc player the type of disc being played.